In general, automotive passenger restraint systems perform a number of functions including acceleration sensing, signal processing and analysis, and deployment of one or more restraint devices such as frontal or side air bags and seat belt pretensioners in response to a sensed crash event. Typically, the acceleration signal is monitored to detect a potential crash event, and then filtered or integrated over the course of the crash event to produce a velocity change or .DELTA.V signal. If the .DELTA.V signal exceeds a threshold, the crash event is determined to be sufficiently severe to warrant deployment of restraints. The threshold is typically time-dependent, and is calibrated based on data logged for different types of crash events, as well as data logged during rough road driving.
There are a number of drawbacks with the above-described approach. For example, it is often difficult to reliably synchronize the time progression of the crash (that is, the event clock or timer) with the actual crash event. This makes it difficult to distinguish between deployment events and non-deployment events, particularly in the first portion of the sensed event. Additionally, it is difficult to deploy restraints quickly enough in certain high speed crash events and localized impacts if the deployment decision is based solely on a detected change in velocity (.DELTA.V) as described above.